Of course, if that were really true, developers of upcoming MMOs that will be in competition with WoW would probably not feel the need to claim it. Especially considering the latest push from Blizzard to add to its already massive 9.3 million active subscriber base using celebrity-hosted dynamic commercials, combined with the buzz for the upcoming expansion Wrath of the Lich King, it is doubtful that WoW will be going into decline any time soon.
In fact, Blizzard's parent company, Vivendi, has continued to show significant increased revenue that is attributed to the success of WoW. Its recent merger with Activision suggests that indeed, professional predictions by investors remain positive.
So why say it at all? Honestly, it's not all wishful thinking. If you head over to these "online communities" such as the official forums, unofficial forums, and even our own comment boxes here at WoW Insider, you will find no shortage of complainants.